S9, E18: After a long night of work on an Ancient device found in Glastonbury England Carter achieves a breakthrough. As Mitchell looks on she activates the device - which unexpectedly shifts them both into a different dimension. Invisible and powerless they can now only observe as their friends try to figure out where they've gone. A distress call from the Sodan warriors interrupts Teal'c and Daniel's search. Teal'c and SG-12 hurry to the Sodan homeworld where a brutal massacre has taken place. The Sodan leader Haikon clings to life as he explains what happened. A Prior of the Ori turned one of the warriors Volnek into an irrational killer. Wearing a Sodan wrist device that makes him invisible Volnek butchered his comrades and is still stalking the area. Because warriors wearing the wrist devices can see each other Teal'c puts on a second device and sets out in pursuit. On Earth Dr. Lee discovers lepton radiation near the Ancient device. Daniel recalling that leptons were associated with his own disappearance into another dimension several years ago delves into Ancient texts recovered in Glastonbury. There he finds a legend about Arthur's Mantle a mythical cloak that made the famous king invisible. The cloak Daniel concludes was actually a medieval metaphor for the Ancient device which allows transportation - and communication - between alternate dimensions.As Carter and Daniel begin a painstaking trans-dimensional conversation Mitchell tags along with a team of reinforcements to the Sodan world. There Teal'c has just confronted Volnek in a desperate battle but Volnek was eerily invincible to gunfire and forced Teal'c to retreat. Meanwhile Dr. Lee activates the Ancient device - mistakenly sending Daniel to the alternate dimension too. Frustrated Daniel nonetheless seizes the chance to read pages of holographic text that the device only displays on this side. He learns that Merlin an Ascended Ancient built the dimensional transporter to keep a critical project secret even from his fellow Ancients. He was designing a weapon to defend his people from the Ori -- a weapon that can kill Ascended beings.